Fixture for furnace brazing spark plugs



p 1962 E. w. PIERCE 3,053,214

FIXTURE FOR FURNACE BRAZING SPARK mugs Filed Aug. 6, 1954 l \\\Zi H 5 a!62212711 .Pzleme Attorney- United States Patent M 3,053,214 FIXT FORFURNACE BRAZING PARK PLUGS Earl W. Pierce, Flint, Mich, assignor toGeneral Motors Corporation, Detroit, Mich, a corporation of DelawareFiled Aug. 6, 1954, Ser. No. 448,3tlil 1 Claim. (Cl. 1l3--99) Thisinvention relates to a fixture for furnace brazing spark plugs and moreparticularly to an angle type shielded plug having brazedinterconnections between the several metal sections of the shell. Thisapplication is a c0ntinuation-in-part of my application Ser. No. 406,171filed January 26, 1954, now Patent 2,875,365.

In the manufacture of angle type spark plugs for aviation use, theshell, the metal structure surrounding the plug insulator and serving asthe electrical shield for the plug, is necessarily formed of at leasttwo parts. One part is positioned about that portion of the insulator inwhich the electrode is located. The second part is positioned about thecable receiving portion of the insulator which extends angularly fromthe electrode portion.

Such shell construction is commonly obtained in the art by brazing orwelding the two tubular shell sections together using varioussaddleshaped butt type joints or matching 45 angle butt type joints. Ithas been found that such butt joints frequently fail under the vibrationand shock encountered in field use as well as in the course of normalhandling for the reason that it is extremely difiicult to obtain auniform and efficient weld or braze on a long joint-line such as resultsfrom this method of production. At the same time, the absence of auniform and continuous braze or weld results in the incompleteelectrical sealing of the plug with the result that the plug producesintolerable electrical interference with the other electrical andcommunications equipment. Likewise, 45 angle construction requires thatthe plug have available on the engine a relatively large head room, theheight of the plug from the engine exterior surface, a condition whichis usually non-existent in aviation usage. Additionally, by reason ofthe difficulties pointed out above, the assembly of each plug is adifiicult and expensive hand operation which is obviously not adaptedfor high volume production requirements.

It is therefore the object of my invention to provide a simple andinexpensive fixture for enabling high volume production of angle typespark plugs.

To attain this objective, I provide a spark plug shell formed of aplurality of telescoping sections which are furnace-brazed to providehigh strength lap joints, the brazing operation being facilitated bymeans of a steel supporting structure in which a plurality of plugs aresupported in such maner as to be out of direct contact there- Furtherobjects and advantages of the present invention will be apparent fromthe following description, reference being had to the accompanyingdrawing wherein a prefered form of the present invention is clearlyshown.

In the drawing:

FIGURE 1 is a plan view with parts broken away of the brazing fixtureand spark plug assembly of my invention.

FIGURE 2 is an enlarged sectional view taken on line 2,2 of FIGURE 1showing the details of construction of the brazing fixture and sparkplug assembly of my invention.

Referring now to the drawing and more particularly to FIGURE 2, there isshown an angle type spark plug ll. Plug 11 comprises a cylindrical mainportion or shell 3 having a longitudinal bore 5 therein, the upperportion 7 thereof being counterbored to form a shoulder 9. The edge ofshoulder 9 is beveled to provide a conical seating ledge 11 having anaxis coincident with the axis of 3,fi53,2l4 Patented Sept. 11, 1962shell 3. The bottom portion 13 of shell 3 serves as the outer or groundelectrode and is annular in configuration. Seating ledge 1]. acts bothto support the spark plug insulator with its tip end concentric with theouter electrode 13 and as an abutment for establishing a seal betweenthe insulator and the shell 3.

Shell 3 is provided with an annular groove 15 on its outer surfaceadjacent shoulder 9 to enable a gas-tight seal between the shell andinsulator by means of the Cico weld process wherein, under the influenceof axial pressure and electrical heating, the shell is thermoplasticallycollapsed in the annular thin wall section of groove 15 to clamp theinsulator on ledge 11.

The upper end of shell 3 adjacent groove 15 is necked down to provide ashoulder 17 on which a metal mounting pad 19 is telescopicallypositioned. Pad 19' serves to provide the means for mounting theassembled plug in the engine and at the same time provides an extensionof the shell 3 for shielding the plug.

The metal plug body and electrical shielding of plug 1 is completed bymeans of the metal shield cap 21 and shield sleeve 23, these elementsbeing shown as telescopically fitted to each other and to pad 19. Thebody portions 3, 19, 21 and 23 are securely attached to each other bybrazing to form a single unitary structure. In assembling the plug, thetelescoping surfaces are coated with a copper brazing paste which, uponbrazing, forms a uniform and substantially perfect seal between thelapped surfaces of the several body portions or with a fluxing pastealone in which case a copper, or other suitable metal, wire ring isapplied at each joint. Though both the braze paste and the flux ringcombination are satisfactory and may be described as brazing materials,I prefer to use a copper wire ring and flux at each of the joints.

It should be here noted that the telescopic assembly of the shellportions 3, 19, 21 and 23 is formed by machining down the outer endsurface of shell 3, cap 21 and sleeve 23. The inner end surface of pad'19 and cap 21 are correspondingly formed to permit the several bodyportions to be sleeved one within the other and form both a lap and buttjoint between the several parts. Such construction results in a largesurface area of contact between the parts which upon brazing forms aplurality of high strength joints. Likewise, the large surface area ofthe brazed joints assures the effective electrical shielding of theplug.

As is clearly shown on the'drawing, the cap 21 abuts the top of theinsulator and cooperates with ledge l1 to clamp the insulator in theplug body and provide a gastight seal therebetween. The cap 21 is ofsuch configuration as to provide, together with mounting pad 19, a sideopening in the plug body in which sleeve 23 is adapted to be positioned,its axis extending transversely to the shell 3.

As is shown in FIGURE 2, a ceramic insulator Z5 having a centerelectrode 27 positioned therein, is mounted within the metal body bymeans of gaskets 49 and 53 in a manner fully described in my co-pendingapplication Ser. No. 406,171, now Patent 2,875,365, in order to positionthe electrode concentric with the bottom portion of the shell 3.Insulator 25 is generally cylindrical in shape and has a generallytapered lower section 29 and a raised upper section 31. A tubularsection 33 extends laterally from the raised section '31. Insulator 25is provided with a substantially concentric bore 35 extending from thefiring end'37 of section 29 to within the upper portion of raisedsection 31. A laterally extending bore substantially concentric withsection 33 is provided to intersect the upper end of bore 35 and form arecess 39 in which a metal contact cap 41 is adapted to be po- 3sitioned. A counterbore 43 is provided in section 33 to receive aninsulated ignition cable 45.

The electrical connection between cable 45 and center electrode 27 isassured by inserting the inner end of the electrode into a correspondingopening in cap 41. The end of the electrode may be either threaded asshown or slotted to form either a threaded or a spring-like frictionconnection with the cap. The conductor 47 of cable 45 is retained incontact with the outer end of cap 41 in any of a number of ways whichare well known in the art and form no part of the present invention. Anyspaces in cap recess 39 and around electrode 27 are filled with a sodiumsilicate-kaolin type cement also well known in the art. The cement actsto both seal and retain the electrode in the insulator.

As described above, a gas-tight seal between the insulator and the shell3 is obtained by applying pres sure to the shield cap 21 to collapse thethin wall portion in the annular groove 15. The cap 21 then acts toclamp the insulator on ledge 11 with the conical portion of the gasket49 therebetween.

In order that the above described spark plug be practical from aproduction standpoint, it was necessary to devise some means forenabling furnace brazing of the assembled structure. I have found that adevice of the type shown in FIGURES =1 and 2. was well suited for thepurpose. The device of my invention comprises a channel-like frame 57shown as consisting of an elongated base plate 59 to each side of whichthere is rigidly secured, as by a plurality of bolts 61, a co-extensiveplate 63. The plates 59 and 63 are formed of any suitable heat-resistantmetal alloy, i.e., a nickel-steel alloy, and are of sufficient thicknessto enable the fixture to withstand brazing temperatures as high as 2200F. without destructive warpage. Reinforcing plates 64 may be used oneach end between the side plates 63 in order to give further strength tothe frame.

Because of the fact that the brazing metal tend to volatilize on passagethrough the brazing furnace, it was found necessary to preventmetal-to-metal contact between the frame 57 and the plug :1 since suchcontacting portions would likewise be brazed together. I have discoveredthat the isolation of the plug 1 may be accomplished by using supportmembers formed of non-metallic material, i.e., ceramics such as aluminaor titania type materials, glass, etc.

As is clearly shown on FIGURE 1, the unbrazed plug assemblies 1 arepositioned crosswise in the frame 57 with the firing end of eachalternate plug on the same side. In this manner, a maximum number ofplug assemblies may be loaded in a given length of frame. Each plugassembly is supported within the frame 57 by means of a ceramicsupporting saddle 65 which is positioned in an aperture provided in thebase plate 59. Each plug assembly is clamped between a pair of axiallybored ceramic bushings 67 and 69 which are positioned in aperturesprovided in each side plate 63, the bushings being in axial alignmentwith each other and in the same axial plane as that of saddle 65.Clamping action is attained by means of a screw 71, one end of which isthreaded for cooperation with a loosely-fitted nut 73 and is adapted tofit within the axial bore provided in the bushings. The other end of thescrew 71 is separated from the threaded portion by means of a radiallyextending flange 74 and is adapted to fit within the axial bore of anannular ceramic disk 75.

The principles of my invention will be readily understood from thefollowing description of the production of a spark plug as shown on thedrawing. The several metal parts of spark plug body 3, 19, 21 and 23,are accurately machined so that their several seating and wall surfacesare concentric and true with the longitudinal axis of shell 3 as well asbeing so dimensioned as to fit together telescopically, sleeve 23 beingat a predetermined angle to shell 3. The angle type ceramic insulator 25is then molded of a suitable heat resisting powder following which themolded blank is fired to sinter it into a composite fused body. Themetal gaskets 49 and 53 are then positioned on the bottom and topportions, respectively, of the upper portion 31 of the insulator 25.Upon turning down these gaskets as described in my co-pendingapplication, the insulator is positioned in the shell 3 with the conicalportion of the gasket 49 squarely on ledge 11 thus positioning thecenter electrode concentric with the firing end of shell 3. Theremaining body parts are then telescopically assembled on the shell andthe assembly is ready for placement in a brazing furnace at about 2000 Fthe interlocking surfaces of the several parts having been previouslycoated with a flux, a copper wire ring being applied at each joint.

Upon positioning the saddle 65 and bushings 67 and 69 in the frame 57,the spark plug is located between the bushings and on the saddle. Theexpansion member, screw 71, is then positioned between the side plates63 and the cap 21 with the threaded follower, nut 73, abutting theceramic bushing and with the head or flange 74 abutting the ceramic disk75 which is interposed between the cap 21 and the screw. Upon threadingthe follower 73 off of screw 71, the plug body portions are tightlyforced together. The frame 57 is then passed through the brazing furnacewhere the temperature is such as to fuse the brazed metal. Upon cooling,the brazed sections are securely interconnected to form a strong,completely shielded, unitary spark plug body.

The gas-tight seal of the insulator 25 within shell 3 is thenaccomplished by mounting the plug 1 in a jig for supporting the shell 3while passing an electric current therethrough at the same time thataxial pressure is applied to shield cap 2 1. A spacer gasket 55 may beused on top of cap 53 when necessary. Contact cap 41 is then insertedinto recess 39 and center electrode 27 is threaded into an openingtherein. All spaces in recess 39 and about electrode 27 are then filledwith a silicate base cement to seal the electrode in the insulator andfix the elements in position to form the completed and compensated plug1.

From the above description, it can be seen that I have provided a simpleand integrally formed shielded angletype spark plug by a method offabrication which permitts the plug to be readily formed on a productionbasis.

While the form of embodiment of the invention as herein disclosedconstitutes a preferred form, it is to be understood that other formsmight be adopted as may come within the scope of the claim whichfollows.

I claim:

A fixture for use in furnace brazing spark plugs having a metal bodyformed of a plurality of separate portions comprising a metal framehaving side and bottom portions, a ceramic saddle positioned in anaperture in said bottom portion for supporting said body out of metalcontact with said frame, a ceramic bushing positioned in an apertureprovided in each side portion of said frame, said bushings being inaxial alignment with each other and in the same axial plane as that ofsaid saddle, a screw positioned on one of said bushings positioned inthe side of said frame with the threaded end in a bore formed therein, athreaded follower on said screw in abutment with said bushing, a flangeon said screw between said follower and the end of the screw adjacentthe body and a ceramic disk positioned on said screw in contact withsaid flange for contact with the body.

References Cited in the file of this patent UNITED STATES PATENTS (Otherreferences on following page) UNITED STATES PATENTS 2,443,574 Burns June15, 1948 1 51 79 A1 d M 29 193,2 2,464,574 g l Mali 1949 2 195 314 gggM2; 2 1940 214799325 De g- 1949 2,209,709 Weatherhead July 30, 1940216181234 Armaccst 1 1952 2,295,996 Lauffenburger Sept. 15, 1942 52,633,116 Ingram 1953 Eve eflt Aug 3, Duck et y 2,332,360 Wakefield 061,19, 1943 2,820,286 Andrus Jail 1958 2,335,343 Sendzimir NOV. 2, 1943FOREIGN PATENTS 2,352,857 Nachemov July 4, 1944 2,366,164 Weick et v11.Jan. 2, 1945 10 260,746 Great W? 11, 1926 2,389,597 Ciprian-i 6161 Nov.27, 1945 Great m? 17: 1944 2 433 339 Brown Dec. 30, 1947 586,325 Great f1947 2,435,448 Kraeft et a1. Feb. 3, 1948 115,784 Austr'aha 26, 19422,437,209 Rabezzana Mar. 2, 1948

